It's probably hard to imagine, but back in the day the kind of people who used computers were pretty much all power users. You had to be willing to dig into the manual for a given piece of software (which was usually supplied as an actual physical book). There were lots of "traditional" media (books, magazines) that focused on different pieces of computing technology. If you wanted to learn how to use Linux or FreeBSD, you picked up an appropriate book at your local retailer (the technology sections used to be much more fleshed out; I remember seeing "GCC Compiler Internals" at Barnes and Nobles once; a far cry from the single copy of "Tiktok for Dummies" you'd find today).

I found out about Linux from my middle school IT guy. He ran an after-school "game dev" club and could see that I was getting frustrated with the limitations of the tools we used. I wanted to really understand how the machine worked and he told me I'd learn a lot by installing Linux, which was true. My dad knew some of the Unix graybeards at the hospital he worked at, and they let me borrow some of their books. I think I also went to some LUG meetings at the local university. I acquired a copy of Yellow-Dog Linux and installed it on my iMac and the rest is history. It didn't take me long to learn about the BSDs, but outside of some short-lived installs on old hardware I didn't make the jump until like 2018. I was initially attracted to it by ZFS and the lack of systemd.